A new discovery that many small galaxies throughout the universe do not 'swarm' around larger ones like bees but instead 'dance' in orderly disc-shaped orbits is a challenge to our understanding of how the universe formed and evolved.
The universe contains billions of galaxies. Some, such as the Milky Way, are immense, containing hundreds of billions of stars. Most galaxies, however, are dwarfs, much smaller and with only a few billion stars.
For decades astronomers have used computer models to predict how these dwarf galaxies should orbit large galaxies. They had always found that they should be scattered randomly.